Add a get_bitfield function for byte arrays.

6 files changed, 110 insertions, 16 deletions

diff --git a/src/bitfield/8byte.c b/src/bitfield/8byte.c
index 76dccc75..3c555f08 100644
--- a/src/bitfield/8byte.c
+++ b/src/bitfield/8byte.c
@@ -8,7 +8,7 @@
 
 uint8_t eightbyte_get_nibble(const uint64_t source, const uint8_t nibble_index,
         const bool data_is_big_endian) {
-    return eightbyte_get_bit_field(source, NIBBLE_SIZE * nibble_index, NIBBLE_SIZE,
+    return eightbyte_get_bitfield(source, NIBBLE_SIZE * nibble_index, NIBBLE_SIZE,
             data_is_big_endian);
 }
 
@@ -20,7 +20,10 @@ uint8_t eightbyte_get_byte(uint64_t source, const uint8_t byte_index,
     return (source >> (EIGHTBYTE_BIT - ((byte_index + 1) * CHAR_BIT))) & 0xFF;
 }
 
-uint64_t eightbyte_get_bit_field(uint64_t source, const uint16_t offset,
+// TODO is this funciton necessary anymore? is it any faster for uint64_t than
+// get_bitfield(data[], ...)? is the performance better on a 32 bit platform
+// like the PIC32?
+uint64_t eightbyte_get_bitfield(uint64_t source, const uint16_t offset,
         const uint16_t bit_count, const bool data_is_big_endian) {
     int startByte = offset / CHAR_BIT;
     int endByte = (offset + bit_count - 1) / CHAR_BIT;
@@ -33,8 +36,7 @@ uint64_t eightbyte_get_bit_field(uint64_t source, const uint16_t offset,
     uint64_t ret = bytes[startByte];
     if(startByte != endByte) {
         // The lowest byte address contains the most significant bit.
-        int i;
-        for(i = startByte + 1; i <= endByte; i++) {
+        for(uint8_t i = startByte + 1; i <= endByte; i++) {
             ret = ret << 8;
             ret = ret | bytes[i];
         }
diff --git a/src/bitfield/8byte.h b/src/bitfield/8byte.h
index 194007c8..ab775caa 100644
--- a/src/bitfield/8byte.h
+++ b/src/bitfield/8byte.h
@@ -32,11 +32,11 @@ extern "C" {
  *
  * Examples
  *
- *  uint64_t value = get_bit_field(data, 2, 4);
+ *  uint64_t value = get_bitfield(data, 2, 4);
  *
  * Returns the value of the requested bit field, right aligned in a uint64_t.
  */
-uint64_t eightbyte_get_bit_field(uint64_t source, const uint16_t offset,
+uint64_t eightbyte_get_bitfield(uint64_t source, const uint16_t offset,
         const uint16_t bit_count, const bool data_is_big_endian);
 
 /* Public: Return a single nibble from the payload, with range checking.
diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c
index 3b0c5fdd..52f368f5 100644
--- a/src/bitfield/bitfield.c
+++ b/src/bitfield/bitfield.c
@@ -2,6 +2,7 @@
 #include <limits.h>
 #include <string.h>
 #include <stddef.h>
+#include <endian.h>
 
 uint64_t bitmask(const uint8_t bit_count) {
     return (((uint64_t)0x1) << bit_count) - 1;
@@ -26,8 +27,25 @@ uint8_t get_byte(const uint8_t source[], const uint8_t source_length,
     return 0;
 }
 
+uint64_t get_bitfield(const uint8_t source[], const uint8_t source_length,
+                const uint16_t offset, const uint16_t bit_count) {
+    if(bit_count > 64 || bit_count < 1) {
+        // TODO error reporting?
+        return 0;
+    }
+
+    union {
+        uint64_t whole;
+        uint8_t bytes[sizeof(uint64_t)];
+    } combined;
+    copy_bits_right_aligned(source, source_length, offset, bit_count,
+            combined.bytes, sizeof(combined.bytes));
+    return htobe64(combined.whole);
+}
+
 bool set_nibble(const uint16_t nibble_index, const uint8_t value,
         uint8_t* destination, const uint16_t destination_length) {
     return copy_bits(&value, CHAR_BIT, NIBBLE_SIZE, NIBBLE_SIZE, destination,
             destination_length, nibble_index * NIBBLE_SIZE);
 }
+
diff --git a/src/bitfield/bitfield.h b/src/bitfield/bitfield.h
index 5dd976f0..80f31243 100644
--- a/src/bitfield/bitfield.h
+++ b/src/bitfield/bitfield.h
@@ -10,6 +10,36 @@
 extern "C" {
 #endif
 
+/* Public: Reads a subset of bits into a uint64_t, right aligned so they may be
+ * interpreted as a number.
+ *
+ * source - the bytes in question.
+ * source_size - the number of bytes in the source.
+ * offset - the starting index of the bit field (beginning from 0).
+ * bit_count - the width of the bit field to extract. This must be less than or
+ *      equal to 64.
+ *
+ * Bit fields are positioned according to big-endian bit layout and the data is
+ * swapped automatically as necessary depending on the compiled architecture.
+ *
+ * For example, the bit layout of the value "42" (i.e. 00101010 set at position
+ * 14 with length 6 is:
+ *
+ *     000000000000001010100000000000000000000000000000000000000000000
+ *
+ * and the same value and position but with length 8 is:
+ *
+ *     000000000000000010101000000000000000000000000000000000000000000
+ *
+ * Examples
+ *
+ *  uint64_t value = get_bitfield(data, data_size, 2, 4);
+ *
+ * Returns the value of the requested bit field, right aligned in a uint64_t.
+ */
+uint64_t get_bits(const uint8_t source[], const uint8_t source_length,
+                const uint16_t offset, const uint16_t bit_count);
+
 /* Public: Return a single nibble from the byte array, with range checking.
  *
  * source - the source byte array.
@@ -142,7 +172,9 @@ bool set_nibble(const uint16_t nibble_index, const uint8_t value,
  */
 uint16_t bits_to_bytes(uint32_t bits);
 
-/* Private:
+/* Public: Return a right aligned bitmask for a uint64_t.
+ *
+ * bit_count - the number of bits to mask, right aligned.
  */
 uint64_t bitmask(const uint8_t bit_count);
 
diff --git a/src/canutil/read.c b/src/canutil/read.c
index 4864a60f..3931721a 100644
--- a/src/canutil/read.c
+++ b/src/canutil/read.c
@@ -4,7 +4,7 @@
 
 float eightbyte_parse_float(uint64_t data, uint8_t bit_offset, uint8_t bit_size,
         float factor, float offset) {
-    uint64_t raw = eightbyte_get_bit_field(data, bit_offset, bit_size, true);
+    uint64_t raw = eightbyte_get_bitfield(data, bit_offset, bit_size, true);
     return raw * factor + offset;
 }
 
@@ -14,9 +14,19 @@ bool eightbyte_parse_bool(uint64_t data, uint8_t bit_offset, uint8_t bit_size,
     return value == 0.0 ? false : true;
 }
 
-float bitfield_parse_float(const uint8_t data[], const uint16_t size,
+float bitfield_parse_float(const uint8_t source[], const uint16_t source_length,
         const uint8_t bit_offset, const uint8_t bit_size, const float factor,
         const float offset) {
-    //TODO
-    return 0;
+    uint64_t raw = get_bitfield(source, source_length, bit_offset, bit_size);
+    // TODO seems dumb that this is repeated from eightbyte_parse_float - is it
+    // really worth keeping around these two implementations?
+    return raw * factor + offset;
+}
+
+float bitfield_parse_bool(const uint8_t source[], const uint16_t source_length,
+        const uint8_t bit_offset, const uint8_t bit_size, const float factor,
+        const float offset) {
+    float value = bitfield_parse_float(source, source_length, bit_offset,
+            bit_size, factor, offset);
+    return value == 0.0 ? false : true;
 }
diff --git a/src/canutil/read.h b/src/canutil/read.h
index bf6c0ade..733e3509 100644
--- a/src/canutil/read.h
+++ b/src/canutil/read.h
@@ -10,7 +10,7 @@ extern "C" {
 
 /* Public: Parse a CAN signal from a message and apply required transformation.
  *
- * data - the payload containing the signal.
+ * source - the payload containing the signal.
  * bit_offset - the starting bit for the signal.
  * bit_size - the width of the signal.
  * factor - the transformation factor for the signal value, applied after
@@ -20,16 +20,30 @@ extern "C" {
  *
  * Returns the decoded and transformed value of the signal.
  */
-float eightbyte_parse_float(const uint64_t data, const uint8_t bit_offset,
+float eightbyte_parse_float(const uint64_t source, const uint8_t bit_offset,
         const uint8_t bit_size, const float factor, const float offset);
 
-float bitfield_parse_float(const uint8_t data[], const uint16_t size,
+/* Public: Parse a CAN signal from a message storage as a byte array and apply
+ * required transformation.
+ *
+ * source - the payload containing the signal.
+ * source_size - the size of the payload in bytes.
+ * bit_offset - the starting bit for the signal.
+ * bit_size - the width of the signal.
+ * factor - the transformation factor for the signal value, applied after
+ *      pulling out the bit field. Use 1.0 for no factor.
+ * offset - the transformation offset for the signal value, applied after
+ *      pulling out the bit field. Use 0 for no offset.
+ *
+ * Returns the decoded and transformed value of the signal.
+ */
+float bitfield_parse_float(const uint8_t source[], const uint16_t source_size,
         const uint8_t bit_offset, const uint8_t bit_size, const float factor,
         const float offset);
 
 /* Public: Parse a CAN signal from a message and interpret it as a boolean.
  *
- * data - the payload containing the signal.
+ * source - the payload containing the signal.
  * bit_offset - the starting bit for the signal.
  * bit_size - the width of the signal.
  * factor - the transformation factor for the signal value, applied after
@@ -39,9 +53,27 @@ float bitfield_parse_float(const uint8_t data[], const uint16_t size,
  *
  * Returns false if the value was 0, otherwise true.
  */
-bool eightbyte_parse_bool(uint64_t data, uint8_t bit_offset, uint8_t bit_size,
+bool eightbyte_parse_bool(uint64_t source, uint8_t bit_offset, uint8_t bit_size,
         float factor, float offset);
 
+/* Public: Parse a CAN signal from a message storage as a byte array and
+ * interpret it as a boolean.
+ *
+ * source - the payload containing the signal.
+ * source_size - the size of the payload in bytes.
+ * bit_offset - the starting bit for the signal.
+ * bit_size - the width of the signal.
+ * factor - the transformation factor for the signal value, applied after
+ *      pulling out the bit field. Use 1.0 for no factor.
+ * offset - the transformation offset for the signal value, applied after
+ *      pulling out the bit field. Use 0 for no offset.
+ *
+ * Returns false if the value was 0, otherwise true.
+ */
+float bitfield_parse_float(const uint8_t source[], const uint16_t source_size,
+        const uint8_t bit_offset, const uint8_t bit_size, const float factor,
+        const float offset);
+
 #ifdef __cplusplus
 }
 #endif